On Molecular And Microscopic Science - free ebook by Mary Somerville

ON MOLECULAR and MICROSCOPIC SCIENCE VOLUME THE FIRST

ON the CONNECTION of the PHYSICAL SCIENCES. 9th Edition. Portrait. Post 8vo. 9 s. PHYSICAL GEOGRAPHY. New Edition, thoroughly revised. Portrait. Post 8vo. [ In the press. Fig. 89, p. 20. EUCYRTIDIUM CRANOIDES. [ Frontispiece to Vol. I....

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ON MOLECULAR AND MICROSCOPIC SCIENCE VOLUME THE SECOND

Fig. 118, p. 107. GALEOLARIA LUTEA. [ Frontispiece to Vol. II....

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SECTION I. FUNCTIONS OF THE ANIMAL FRAME.

Although animal life is only known to us as a manifestation of divine power not to be explained, yet the various phases of life, growth, and structure in animals, from the microscopic Monad to Man, are legitimate subjects of physical inquiry, being totally independent of those high moral and religious sentiments which are peculiar to Man alone. The same simple elements chemically combined in definite but different proportions form the base of animal as well as of vegetable life. But besides the

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PREFACE.

Microscopic investigation of organic and inorganic matter is so peculiarly characteristic of the actual state of science, that the Author has ventured to give a sketch of some of the most prominent discoveries in the life and structure of the lower vegetable and marine animals in addition to a few of those regarding inert matter. The Author feels bound to return her best thanks to kind friends—Sir John Herschel, Mr. Huggins, Mr. Gwyn Jeffrey, Prof. Tyndall, and Mr. T. Moore of Chelsea, who have

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SECTION I. ELEMENTARY CONSTITUTION OF MATTER.

The investigations which have revealed the most refined and wonderful relations between light, heat, electricity, and highly elastic media; the relation of these powers to the particles of solid and liquid matter, new methods of analysis, and the microscopic examination of that marvellous creation, animal and vegetable, which is invisible to the unaided eye of man, have brought a new accession to the indefinitely small within the limits of modern science. Wherever the astronomer has penetrated i

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Class I.—Rhizopoda.

The Amœba, which is the simplest of the group, is merely a mass of semi-fluid jelly, ‘changing itself into a greater variety of forms than the fabled Proteus, laying hold of its food without members, swallowing it without a mouth, digesting it without a stomach, appropriating its nutritious material without absorbent vessels or a circulating system, moving from place to place without muscles, feeling (if it has any power to do so) without nerves, multiplying itself without eggs, and not only thi

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Class II.—Foraminifera.

The geological importance of the Foraminifera, their intrinsic beauty, the prodigious variety of their forms, their incredible multitude, and the peculiarity of their structure, have given these microscopic organisms the highest place in the class of Rhizopods. The body of these animals consists of a perfectly homogeneous sarcode or semi-fluid protoplasm, showing no tendency whatever to any film or surface-layer. It is inclosed in a shell; and the only evidence of vitality that the creature give

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SECTION II. ON FORCE, AND THE RELATIONS BETWEEN FORCE AND MATTER.

Force is only known to us as a manifestation of divine power which can neither be created nor destroyed. The store of force or energy in nature is ever changing its form of action, its amount never. It may be dispersed in various directions, and subdivided so as to become evanescent to our perceptions; it may be balanced so as to be in abeyance, or it may become potential as in static electricity; but the instant the impediment is removed the power is manifested by motion. Whatever form force ma

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Order of Porcellanous Foraminifera.

The Miliolidæ constitute the porcellanous order, which consists of twelve genera and many species, varying from a mere scale to such as have chambered shells of complicated structure. The genus Miliola has minute white shells resembling millet seeds, often so brilliantly polished that they are perfectly characteristic of the porcelain family to which they belong. No Foraminifera are better suited to give an idea of the intimate connection between the shell and its inhabitant than the Miliola, th

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SECTION III. ATOMIC THEORY, ANALYSIS AND SYNTHESIS OF MATTER, UTILITY OF WASTE SUBSTANCES—COAL-TAR COLOURS, ETC.

The chemical combination which forms the infinite variety of substances in the organic and inorganic creation consists in an intimate union of their ultimate atoms which produces substances differing from their constituent parts in every respect except gravitation, the sum of the weights of their constituent parts being invariably equal to the weight of the resulting substance. Thus the chemical union of oxygen and hydrogen forms water, and the weight of the water so formed is exactly equal to t

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SECTION IV. THE SOLAR SPECTRUM, SPECTRUM ANALYSIS, SPECTRA OF GASES AND VOLATILIZED MATTER, INVERSION OF COLOURED LINES, CONSTITUTION OF SUN AND STARS.

To the unrivalled genius of Sir Isaac Newton we owe the solar spectrum, and the laws of coloured rings, by aid of which, Dr. Thomas Young proved and established the undulatory theory which forms the basis of the whole science of light. The visible part of the solar spectrum forming a band of seven colours was supposed to be continuous till the year 1802, when Dr. Wollaston looking with a prism whose axis was parallel to a narrow slit in a window shutter, at a sunbeam passing through it, discover

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Order of Arenaceous Foraminifera.

In the numerous family of Lituolidæ the abode of the animal consists of a cement mixed with very fine particles of sand with larger ones imbedded in the surface. The order includes a wide range of forms divided into three genera, the simplest of which consists of a cylindrical tube twisted into a spiral gradually increasing in diameter, and attached to a foreign substance by one of its surfaces. The creature which lives in it is a uniform cord of sarcode, which sends its pseudopodia out through

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Order of Vitreous Foraminifera.

Nearly all the Foraminifera on the British coasts belong to the Vitreous or Perforated order, which consists of three natural families and many genera. Their shells are vitreous, hyaline, and generally colourless, even although the substance of the animal is deeply coloured; in some species both the animal and its shell are of a rich crimson. The glassy transparency of the shells would be perfect were they not perforated by numerous tubes running from the interior of the chambers straight throug

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SECTION I. MICROSCOPIC STRUCTURE OF THE VEGETABLE WORLD.

The study of the indefinitely small in the vegetable and animal creation, is as interesting as the relation between the powers of nature and the particles of matter. The intimate organic structure of the vegetable world consists of a great variety of different textures indeterminable by the naked eye, and for the most part requiring a very high magnifying power to discriminate. But ultimate analysis has shown that vegetables are chemical combinations of a few very simple substances. Carbon and t

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SECTION II. ALGÆ.

The principal objects in the study of plant-life are the organs by means of which they obtain and assimilate substances that are essential for their nourishment and growth, and those by which the perpetuity of their race is maintained and their type transmitted from age to age. In the lowest group of plants, represented by the Algæ, which come first into consideration, the two properties are combined; in the highest they are distinctly different, but the progress from one to the other may be tra

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Class III.—Sponges.

According to the observations of Mr. Carter, sponges begin their lives as solitary Amœbæ which grow by multiplication into masses, and assume endless forms according to the species; turbinate, bell-shaped, like a vase, a crater, a fan, flat, foliaceous and lobed or branching and incrusting the surface of stones. All the Amœbæ are so connected as to form one compound animal. The whole substance of a sponge is permeated by innumerable tubes which begin in small pores on the surface, and continuall

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Class IV.—Infusoria.

The Infusoria, which form the second group of the Protozoa, are microscopic animals of a higher grade than any of the preceding creatures, although they go through their whole lives as isolated single cells of innumerable forms. They invariably appear in stagnant pools and infusions of animal and vegetable matter when in a state of rapid decomposition. Every drop of the green matter that mantles the surface of pools in summer teems with the most minute and varied forms of animal life. The specie

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SECTION III. FUNGI.

The Fungi are enormously numerous. No less than 2,000 of the highest and most conspicuous of these plants have been figured; many more have been described; multitudes of those inhabiting the torrid zone are unknown; and the microscopic and parasitic tribes are innumerable. Though with a few exceptions entirely formed of cellular tissue, the fungi resemble animals in respiration and chemical constitution. They contain more azote than any other of the Cryptogamia, and obtain it chiefly from their

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Ciliograde Hydrozoa.

The ciliograde Acalephæ, which form four orders and many genera, and which swim by means of symmetrical rows of long cilia, are represented on the British coasts by the Cydippe pileus and the Beroë Forskalia ( fig. 116 ), little delicately tinted, gelatinous, and transparent animals that shine in the dark. The Cydippe pileus is a globe three-eighths of an inch in diameter, like the purest crystal, with eight bands of large cilia, stretching at regular distances from pole to pole. A mouth, surrou

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SECTION IV. LICHENS.

Lichens are essentially air plants, being nourished, like the Algæ, by the medium in which they grow. They vary from a pulverulent or dry papillose crust, to a leathery or horny expansion, and even acquire an erect stem. They are independent of the matrix to which they are attached. Hence they spread their coloured frond, or thallus, in circular or indefinite patches on old walls, the tiles of houses, stones, and rocks. They appear in large expansions of red, golden yellow, grey or white, on bar

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SECTION V. CHARACEÆ.

Fig. 40. Nitella flexilis. The Characeæ are submerged annual water plants, growing in stagnant pools and ditches rather than in running streams. It is a small order containing but three genera, but the numerous species are dispersed all over the world, especially in temperate climates. The genera found in this country are Nitella and Chara. The Nitella flexilis ( fig. 40 ) may be taken as a representative of the order. Its stem or axis is formed of very long cylindrical transparent tubes, joined

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Campanograde Acalephæ.

There is a group of oceanic Hydrozoa, consisting of several families, which are fed by numerous suctorial organs called polypites, with tentacula and thread-cells attached to their bodies, so that they are analogous to the marine hydræ, in being colonies of individuals united into a compound animal. Some have air-vessels, which enable them to float on the surface of the water; but the locomotive organs of this group are bells, so that they may be called Campanograde Acalephæ. The family of the D

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SECTION VI. HEPATICÆ, OR LIVERWORTS.

The Hepaticæ are the small herbaceous plants, which constitute the three distinct natural orders called respectively Ricciaceæ, Marchantiaceæ, and Jungermanniaceæ. They are distinguished primarily by the first having the sporangia valveless, without elaters; by the second having dependent valvate or irregularly bursting sporangia; and by the third having the sporangia valvate and erect. Both the latter, moreover, have the spores mixed with elaters. The Ricciaceæ, popularly called Crystalworts, w

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Physograde Acalephæ.

The Galeolaria lutea ( fig. 118 , frontispiece) is similar to the Praya diphys in having a slender, tubular body, with groups of sterile polypites and their appendages hanging at intervals along its under-side like a fringe, and also in having two swimming-bells at its anterior extremity; but it has no special small bells. The large ones differ from each other in size, form, and position. The largest is nearly cylindrical, its mouth is turned upwards, and its rim is elevated at one part into two

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SECTION VII. MUSCI, OR MOSSES.

Mosses approach the higher classes of vegetable life in having roots, and a more or less upright stem or axis of growth. Like all other plants, they are chiefly formed of cellular tissue, yet, in the stems, there is an indication of a separation between the bark and pith by the intervention of a circle of elongated cells approaching to woody fibre, which passing into the branches and leaves form a kind of midrib, either extending to the extremity of the leaf or not. The delicate little leaves, w

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Alcyon Zoophytes.

The Alcyon zoophytes comprise the Alcyons, Gorgons, and Pennatulidæ, or sea-pens. The polypes are of the same form in all, and are united by a fleshy or horny substance into large communities, so connected and mutually dependent as to constitute one compound animal. Figure 123 represents a highly magnified group of Alcyonian polypes in different stages of expansion. The body of the polype is soft, contractile, and composed of thin, delicate transparent tissues. It has the form of a cone resting

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SECTION VIII. FILICES, OR FERNS.

Of all the spore-bearing families, the Ferns are the most universally known. They may easily be recognized by the coiling inwards of their young leaves in spring previous to expansion, and by the arrangement of the fruit on their undersides when expanded. The Ferns are exceedingly numerous both in genera and species, and vary from low herbaceous plants of an inch high, to trees with upright trunks forty or fifty feet or more in height, bearing a graceful coronet of leaves at their extremity. The

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Actinian Zoophytes.

The great family of the Actinian zoophytes abounds in genera and species. The common Sea Anemone, or Actinia, of which there are more than seventy species on the British coasts, is the model of the minute polypes which inhabit the stony corals, and build the coral reefs and atolls of the tropical Pacific. The Sea Anemone has a cylindrical body, attached at one end by a sucker to rocks or stones at no great depth, and a flat circular disk at the other, with the mouth in its centre: the mouth, whi

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SECTION IX. EQUISETACEÆ, OR HORSETAILS.

The Equiseta are leafless, herbaceous plants, annually renewed from a creeping rhizome, and growing in marshy land, in pools and ditches, on the banks of rivulets, and in rivers, from Lapland and Siberia to within the tropics. There is but one genus, and few species. The largest of the ten or eleven species, which are indigenous in Great Britain, is not more than five or six feet high, but they are of greater size in warm climates. The Horsetails begin their lives precisely like the Ferns; for,

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Entozoa.

There are three genera and numerous species of Entozoa. Every animal has one or more species peculiar to itself; fourteen infest the human race. They have a soft, absorbent body of a white or whitish colour, in consequence of being excluded from light, and living as they do by absorbing the vitalized juices of the animals they infest. Their nutritive system is in the lowest state of development; yet there are some of a higher grade. All are remarkable for their vast productiveness. The Tænioïdæ,

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SECTION X. MARSILEACEÆ, OR RHIZOSPERMÆ.

Fig. 71. Pilularia minuta:— a , mature plant, natural size; b , receptacle, slightly magnified. The Marsileaceæ, a natural tribe of small perennial aquatic herbs, have a filiform creeping rhizome with alternate erect leaves, curled in vernation like those of the ferns. The sporangia are enclosed in oval or spherical leathery capsules, or receptacles, which contain two dissimilar forms of reproductive organs—sporangia and antheridia, and are sessile, or nearly so, on the rhizome at the base of th

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Turbellariæ.

The Turbellariæ are fresh- and salt-water animals, distinguished by having the whole surface of their bodies covered by cilia, under which in some species there are thread-cells containing six, eight, or a greater number of darts. Most of the members of this tribe have elongated flattened bodies, and move by a sort of crawling or gliding motion over the surface of aquatic plants and animals. Some of the smaller kinds are sufficiently transparent to allow their internal structure to be seen by tr

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Annelids.

The Annelids are the most highly organized of all the worm tribe. They are exceedingly numerous and varied; some are inhabitants of fresh water, others are terrestrial, but by far the greater number and most highly endowed are marine. They generally have a long, soft, and smooth body, divided or marked by transverse rings into a succession of similar segments. In many the first and last segments are alike; in others the first segment can scarcely be called a head, though it exercises several fun

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SECTION XI. LYCOPODIACEÆ, OR CLUB MOSSES.

The Club Mosses are mostly perennial plants, with slender creeping stems, often several feet or yards in length, occasionally erect, and clothed by small, sessile, closely set, often imbricated leaves without veins. They have in some instances a habit resembling that of Conifers. The stems consist of a mass of thick-walled, often dotted cells, enclosing one or many bunches of scalariform tissue, which sends off branches to every leaf and bud. The scalariform tissue is accompanied by fine, elonga

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SECTION XII. GENERAL STRUCTURE OF FLOWERING PLANTS.

In some of the Cryptogamic families fertilization takes place before the plant itself is developed. In the two highest classes, those containing the great groups of Flowering Plants, on the contrary, it is the ultimate result of the inflorescence, which consists of calyx, corolla, stamens, and pistils, all which are the later expansions of the cellular tissues and groups of vessels which have in earlier stages of development formed the leaves. They contain the same materials, and in fact they ar

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Tardigrada.

The Tardigrades are slow creeping animalcules, which seem to form a link between the Worms and the Rotifers, though they are more nearly allied to the former in having a vermiform body divided transversely into five segments, the first of which is the head, and each of the others has a pair of little fleshy protuberances furnished with four curled hooks. They resemble the Rotifers in their jaws, in their general grade of organization, and in the extreme length of time they can remain dried up wi

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SECTION XIII. MONOCOTYLEDONOUS, OR ENDOGENOUS PLANTS.

The structure, growth, and reproduction of the flower-bearing vegetation offer objects of the highest interest, though very different from those furnished by the flowerless class. The plants whose seeds have but one lobe form a transition from the lowest to the highest class of vegetables, and include those which furnish the principal articles of food to man and animals. They are all flower-bearing, and consist of numerous families of land and water plants. The most important are the palms, whic

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Rotifera.

Although the Rotifera are microscopic objects, their organization is higher than that of the Annelida in some respects. They are minute animalcules, which appear in vegetable infusions and in sea-water, but by far the greater number are found in fresh-water pools long exposed to the air: occasionally they appear in enormous numbers in cisterns which have neither shelter nor cover; a few can live in moist earth, and sometimes individuals are seen in the large cells of the Sphagnum or Bog-Moss. Th

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Echinodermata Asteroïdea.

The Asteroïdea, or Star-Fishes, which are the highest order, form two natural families, the Stelleridæ and Ophiuridæ, which comprise twenty-two genera. The simplest form of the Stelleridæ is the common star-fish, with its flat regularly five-sided disk. A tough membrane, strengthened by reticulated calcareous matter, covers the back, and bends down along the sides, while the under-side of the body or disk, on which the animal creeps, is soft and leathery, with the mouth in its centre. In the oth

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SECTION XIV. DICOTYLEDONOUS, OR EXOGENOUS PLANTS.

In Endogenous plants the seeds have but one lobe, and the growth is invariably from the interior. In the Exogenous class, on the contrary, the seeds have two lobes, and the increase in growth is external: hence the botanical distinction of Exogenous plants. Although the distinctive character of the highest class of vegetables is to have seeds with two lobes, yet the structure and position of the seeds are extremely diversified. Many have horny coats, such as the pips of apples and oranges; or ha

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Echinodermata Crinoïdea.

The Crinoid Echinoderms, or Stone-Lilies, are like a tulip or lily on an upright stem, which is firmly fixed to a substance at the bottom of the sea. During the Jurassic period, miniature forests of these beautiful animals flourished on the surface of the Oolite strata, then under the ocean. Myriads of their fossil remains are entombed in the seas, and extensive strata of marble are chiefly composed of them. Their hollow joints are known in several parts of England as wheel stones, and as St. Cu

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Echinodermata Echinoïdea.

The family of Echinidæ, commonly known as Sea-Eggs or Sea-Urchins, have a beautiful but complicated structure. The calcareous shell of an Echinus is a hollow spheroid with large circular openings at each pole. In the larger of the two, called the corona, the mouth of the animal is situated; in the lesser circle the vent is placed. The spheroid itself is formed of ten bands extending in a meridional direction from the corona to the lower ring; that is, from one polar circle to the other. Each ban

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Echinodermata Holothuroïdea.

The Holothuridæ, or Sea-Cucumbers, are of a higher organization than the preceding Echinoderms. They are soft, worm-shaped, five-sided animals, covered by a flexible, leathery integument or skin, in which are imbedded a vast multitude of microscopic calcareous plates of reticulated structure. The mouth, which is placed at one end of the animal, is surrounded by ten bony plates forming a lantern, analogous to that of the Echinus; they support branching, tubular, and retractile tentacles, which en

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Echinodermata Synaptidæ.

The Synaptidæ are five-sided creatures, similar in structure to the Holothuriæ, though more worm-like. The whole order, which consists of the two genera of Synapta and Chirodota, have twelve calcareous plates round the mouth, five of which are perforated for the passage of the vascular water canals, which convey the liquid for the protrusion of the feet. Fig. 144. Skeleton of Synapta. The calcareous particles imbedded in the skin of the genus Synapta are anchor-shaped spicules fixed to elliptica

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Echinodermata Sipunculidæ.

The Sipunculidæ, which form the last order of the Echinoderms, consist of several genera of marine worm-shaped animals which burrow in the sand, and form a link between the Holothuridæ and the true sea-worms. They have no calcareous particles in their flexible skins, nor have they any tubular feet, or special respiratory organs, but a vascular liquid is kept in motion in the internal cavity by the cilia with which it is lined. The mouth of the Sipunculus is a kind of proboscis with a circular fr

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Macrura.

The body of the Macrura, or long-tailed crustaceans, consists of a number of segments or rings joined end to end, having jointed members on each side. Every individual joint is covered with a hard crust to afford support to the muscles. A certain number of the rings, which form the tail, are always distinct, similar, and movable on one another, whilst the remainder, which form the carapace or shell, are confluent so as entirely to obliterate the divisions. But generally the arrangement of these

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Brachyura.

The Brachyura surpass all the other Decapods in compactness and concentration, and are without exception the highest of the Crustacea. Though apparently without a tail, they really have one, as their name implies; but it is short, rudimentary, and folded under the posterior end of the carapace. The genera and species are exceedingly numerous, many swim and inhabit the deep oceans, others live on the coasts but never leave the water; a numerous tribe live as much in the air as in the water, hidin

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Anomura.

The Anomura is a family of Decapods intermediate between the long and short-tailed Crustacea. There are nine or ten genera and many species, chiefly distinguished by the development of the head and thorax, and the softness of a non-locomotive tail: of these the Pagurus, or Hermit crab, is assumed as the type or representative. The carapace is long and convex, scarcely extending over the basal joints of the feet. The claw feet are short, with a very broad hand and sharp pincers; but the Hermit cr

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Stomapoda.

The Stomapods are all swimmers; they have long bodies with a carapace; but it is so varied in form and size, that no general description of it can be given. They have external, instead of internal, organs of respiration; gills in the form of tufts are in some cases attached to a few of the foot-jaws, but they are much more frequently fixed to the basal joints of their swimming feet, so that the blood in their capillary veins is aërated through their thin skin as they float in the water. In the S

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Amphipoda.

The Amphipods are very numerous, and abound in the British seas. They have long, slender, and many-jointed bodies which have no carapace: the tail in some genera is more fitted for swimming, in others for leaping. The Talitrus, or Sandhopper, common on every sandy shore in Europe, is a well-known example of the leaping genus. It is very small and exceedingly active. The upper antennæ are very short, the inferior pair are large, and longer than the whole body. The anterior feet are thin and not p

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Isopoda.

The order of Isopoda are so called because of the sharp and equal claws of their walking feet, which are often prehensile. Their body is short and flattened, and their small head is almost always distinct from the throat. They are very numerous, and are divided into walking, swimming, and sedentary animals; the females have horny plates on some of their feet, which fold under the throat and form a pouch, in which the eggs are hatched. The Oniscus, common Wood-louse, or Slater, is a terrestrial I

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Entomostraca.

The Entomostraca form an immense group of the lower Crustacea, consisting of five orders. A vast number are just visible to the naked eye, and many are microscopic; they teem in every climate along the coasts, and in the deep blue oceans. The horny coat, enclosing the minute bodies of these animals, is often so transparent that their internal structure, and occasionally the process of the assimilation of the food, is distinctly seen by the aid of a microscope. Small as they are, their beauty is

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Copepoda.

The first order, Copepoda, or oar-footed tribe, have a distinctly articulated body formed of movable rings, bristly swimming limbs; and the females carry their eggs in huge pouches suspended on each side of the posterior part of their bodies. The Sapphirina fulgens is a beautiful example of the two-eyed tribe; its body is nearly oval, divided into nine distinct joints, and so flat that it is almost foliacious. The head has two brilliantly coloured eyes, with large cornea so connected with the sh

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Phyllopoda.

The second order of gill-footed Crustacea are called Phyllopoda, because they have gills like the leaves of a book attached to their lamelliform swimming feet. Their bodies are divided into many segments, and they form two groups, one of which has a carapace, the other has not. The Apus cancriformis is an example of the first. It is about two inches and a half long, and is a large animal compared with the others of its class. Its head and thorax are covered by an oval carapace, and its cylindric

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Pycnogonoïdea or Spider Crabs.

Some of the Spider crabs hook themselves to fishes, while others live under stones, or sprawl with their long hairy legs over sea-weeds, and feed on the gelatinous matter these weeds afford. The throat with its members, and the head soldered to its first ring, forms nearly the whole animal. It has a pair of antennæ and four rudimentary eyes, set on a tubercule. A proboscis-like projection extends from the front; the mouth is furnished with cilia and one pair of foot-jaws. Four pairs of long hair

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Fossil Crustacea.

Analogues to the Anomura are found in the Chalk formation, but the Macrura are the prevailing forms. Extinct species of lobster, crawfish, and shrimps are met with in the secondary strata, from the Chalk to the Coal measures. In the Coal formation all these higher forms disappear, but then the gigantic King Crab, or Limulus, is found accompanied by the minute Entomostracan forms in infinite variety of species....

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Epizoa, or Suctorial Crustacea.

The Epizoa infest the skin, eyes, and gills of fishes. Many of them in their adult state bear a strong resemblance to the lowest of the Crustacea; but, in general, the resemblance between these two classes of animals can only be traced during the extraordinary changes which the Epizoa undergo in their early life, and they differ so much in their perfect state that it is wonderful any connection should ever have been discovered between them. The Epizoa are extremely varied in their perfect forms,

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SECTION VIII. CIRRIPEDIA.

The metamorphoses of the Cirripeds, and their resemblance to the lower Crustacea at each moult, are still more remarkable than those of the Epizoa. They form two primary groups, the Balanidæ, or Acorn shells, and the Barnacles or Lepadidæ, which have peduncles or stalks. Both are parasites, but they do not draw their sustenance from the substances they adhere to. Fig. 153. Balanus culcatus. The Balanidæ ( fig. 153 ) are grouped in innumerable multitudes, crowded together on the rocks of the sout

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SECTION IX. BRYOZOA, OR POLYZOA.

A Bryozoon is a microscopic polype, inclosed in an open horny or calcareous sheath, out of which it can protrude and draw in the anterior part of its body. It is seldom or never seen alone, on account of its tendency to propagate by budding. When the buds spring from the sides of the sheath or cell, it is known as the Sea Mat, or Flustra. The Flustra, which is common on our coasts, spreads its hexagonal cells like a delicate network over sea-weeds, shells and other marine substances. Sometimes t

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Pyrosomidæ.

The Pyrosomidæ are floating compound Ascidians, composed of innumerable individual animals united side by side, and grouped in whorls so as to form a hollow tube or cylinder open at one end only, and from two to fourteen inches long, with a circumference varying from half an inch to three inches. The inhalent orifices of the component animals are all on the exterior of the cylinder, while the exhalent orifices are all on its inside, and the result of so many little currents of water discharged i

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Salpidæ.

The Salpidæ are another family of free-swimming Ascidians. The tunic is perfectly hyaline, the body is somewhat cylindrical, but compressed and open at both ends ( fig. 163 ). The mouth is a slit, the discharging orifice is tubular and can be opened and shut. The breathing apparatus is in the form of a ribbon extending obliquely across the cavity of the tunic, the ear with four otolites is in the ventral fold, and the flux of the pale blood is alternate as in other Tunicata. Fig. 163. Salpa maxi

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Shells of the Mollusca.

When these mollusks come into the water, they soon find their transparent white shell too small, and begin to increase its size by means of the mantle, which is an exquisitely sensible fleshy envelope applied to the back of the animal, extending round its sides like a cloak, only meeting in front, and it is for the most part in close contact with the whole interior of the shell. Its edges are fringed with rows of slender tentacles, and studded with glands, which secrete the colours afterwards se

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Naked Cephalopods.

The Naked Cephalopods have an internal skeleton instead of a shell, in the shape of a transparent horny pen in the Calamary, or the well-known internal shell of the Cuttle Fish; they are divided into Octopods and Decapods, according to the number of their tentacles: the Poulpe, or Octopus vulgaris, is a type of the first, the Sepia or Cuttle Fish, fig. 179 , and the Loligo vulgare or Squid, are types of the last. These creatures may be seen on rocky coasts, or in the ocean hundreds of miles dist

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RECAPITULATION.

Numerous instances of microscopic structure may be found in the vertebrate series of marine animals, but the field is too extensive for the Author to venture upon. In the first section of this book, an attempt has been made to give some idea of the present state of molecular science—far short, indeed, of so extensive a subject; yet it may be sufficient, perhaps, to show the views now entertained with regard to the powers of nature, the atoms of matter, and the general laws resulting from the phe

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FOREIGN HANDBOOKS.

HAND-BOOK—TRAVEL-TALK. English, French, German, and Italian. 18mo. 3 s. 6 d. HAND-BOOK—NORTH GERMANY,— Holland , Belgium , Prussia , and the Rhine from Holland to Switzerland. Map. Post 8vo. 10 s. HAND-BOOK—SOUTH GERMANY, Bavaria, Austria, Styria, Salzberg, the Austrian and Bavarian Alps, the Tyrol, Hungary, and the Danube, from Ulm to the Black Sea. Map. Post 8vo. 10 s. HAND-BOOK—KNAPSACK GUIDE TO THE TYROL. Post 8vo. 6 s. HAND-BOOK—PAINTING. German, Flemish, and Dutch Schools. Woodcuts. 2 Vols

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ENGLISH HAND-BOOKS.

HAND-BOOK—MODERN LONDON. Map. 16mo. 3 s. 6 d. HAND-BOOK—WESTMINSTER ABBEY. Woodcuts. 16mo. 1 s. HAND-BOOK—KENT AND SUSSEX, Canterbury, Dover, Ramsgate, Sheerness, Rochester, Chatham, Woolwich, Brighton, Chichester, Worthing, Hastings, Lewes, Arundel, &amp;c. Map. Post 8vo. 10 s. HAND-BOOK—SURREY AND HANTS, Kingston, Croydon, Reigate, Guildford, Winchester, Southampton, Portsmouth, and Isle of Wight . Maps. Post 8vo. 10 s. HAND-BOOK—WILTS, DORSET, AND SOMERSET, Salisbury, Chippenham, Weymouth

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